Flexible blade fan



Dec. 6, 1966 T. J. WEIR 3,

FLEXIBLE BLADE FAN Filed May 10, 1965 Flg. 3 0

INVENTOR. THOMAS J. WE\R WWV SMMM 4 1 lame us United States Patent ()fitice 3,289,924 Patented Dec. 6, 1966 3,289,924 FLEXIBLE BLADE FAN Thomas J. Weir, Indianapolis, Ind., assignor to William Wallace Corporation, Wilmington, DeL, a corporation of Delaware Filed May 10, 1965, Ser. No. 454,458 2 Claims. (Cl. 230-134) This invention relates generally to air moving fans and in particular to a fan for cooling an internal combustion engine, the pitch of the fan blades 'being automatically reduced as the speed of the fan increases.

Since the volume of air moved by a fan increases as the first power of the fan speed, at high engine speeds the fan may move more air than necessary to cool the engine thus wasting power. Further, under these conditions, the noise level of the fan, which increases substantially with speed, will be unnecessarily high. A solution to this problem, not unknown in the prior art, is to provide the fan with flexible blades which distort with increases in fan speed to a shape of reduced pitch thereby unloading the fan, that is, lowering the volume of air displaced per fan revolution. Such a flexible bladed fan is disclosed in US. Patent 2,032,224. The areas in which the fan spider arms and their respective flexible blades are joined are subject to stresses of almost constantly varying magnitude. Use of rivets or weldments to join these elements, however, provides areas of undesirable stress concentration.

It is an object of the present invention to provide a fan utilizing flexible blades which unload with increasing fan speed but which does not expose the flexible blades to high stress concentrations.

This and other objects will become apparent as the description proceeds with reference to the accompanying drawings in which:

FIG. 1 is a front view of a fan assembly embodying the present invention.

FIG. 2 is a fragmentary, side vie-w illustrating in detall the construction of the junction between the fan blades and the spider of FIG. 1.

FIG. 3 is a side, sectional view of a modified form of the mounting for the flexible fan blades.

Referring to the drawings, the fan assembly includes a spider having a hub portion 11 and a series of radially extending arms 12. The hub portion may be apertured as indicated at 13 for attachment to a driving pulley, and the arms 12 may, as indicated in FIG. 1, be spaced at various angles with respect to each other.

Referring now primarily to FIG. 2, each of the arms carries a flexible fan blade 14. Between each of the blades 14 and its corresponding spider arm 12 is a clamp member 17 which extends beyond the ends of the arms as will be apparent in FIG. 1.

Each of the clamp members 17 is generally U-shaped in cross-section with the area of junction of its legs adjacent the leading edge of 12a of its respective arm 12. A backing plate 18 lies adjacent to each of the fan blades and extends into its clamp member 17. Rivets 21 are spaced along the length of the spider arm and serve to rigidly join the arm, clamp member, blade and backing plate. The backing plate 18 deflects, under load, with the fan blade 14 as will subsequently be described.

As the fan is rotated clockwise as viewed in FIG. 1 at relatively low rotational speeds, the fan blades 14 will be acted on by a force tending to deflect or bend the blades in the direction of the arrow shown in FIG. 2. If this force is of sufficient magnitude, the backing plates 18 will also deflect somewhat. As the speed of rotation of the fan increases, this deflecting force becomes larger and the blades 14 tend to flatten or unload.

Visualized in cross-section, each of the blades can be considered to be a cantilever beam with the clamp being provided at the rivets 21, the beam being under a uniformly distributed load. In prior art flexible blade fan structures omitting the hacking plate, the stress distribution across the width of the fan blade follows that of a cantilever beam, fixed or clamped at one end and under a uniformly distributed load, that is, the stress is zero at the free tip of the beam and then varies exponentially to a maximum at the fixed end of the beam. Maximum stress thus concentrates at the rivet =or weldment (clamp) area in these prior art structures. The presence of the backing plate 18 in the structure of the present invention serves to, in effect, increase the cross-section of the beam formed by the blade along a portion of its length nearest its clamped end. This more uniformly distributes the total stress, along the width of the blade and avoids the high concentration of stress at the riveted or welded attachment of the blade to the spider arm which is characteristic of the prior art structures. The more uniform distribution of stresses across the width of the flexible fan blades, which is inherent in the stnloture of the present invention, results in a substantially improved service life for the blades. Further, because of differences in the application of the deflecting load, as the blade 14- and backing plate 18 deflect, they move slightly relative to each other and this relative motion has a damping effect on blade vibration at resonant fan speeds.

In the modified construction of FIG. 3, the hacking plate 18a differs from backing plate 18 of FIG. 2 in that its marginal area 18b is flanged outwardly somewhat away from the blade 14. This arrangement limits deflection of the blade and provides further reinforcement at maximum deflection conditions, the position assumed by the blade and backing plate under these conditions being shown in broken lines in FIG. 3.

While the invention has been disclosed and described in some detail in the drawings and foregoing description, they are to be considered as illustrative and not restrictive in character, as other modifications may readily suggest themselves to persons skilled in this art and within the broad scope of the invention, reference being had to the appended claims.

The invention claimed is:

1. A fan structure including a spider having arms extending radially outward from a central hub portion, clamp members overlying one face of each of said arms and extending beyond the ends of said arms, each of said clamp members having its marginal portion adjacent the leading edge of its respective arm folded upon itself to provide a generally U-shaped configuration, a flexible fan blade extending into each of said clamp members, a backing plate overlying each of said blades and extending into said clamp member and substantially to the trailing edge of the arm, and fastening means spaced along the length of each arm to rigidly join the arm, clamp member, blade and backing plate, whereby stress in the blades to flexing of the blades and the backing plates is more evenly distributed across the width of the blade and stress concentration at said fastening means is avoided.

2. A fan structure including a spider having arms extending radially outward from a central hub portion, clamp members overlying one face of each of said arms and extend-ing beyond the ends of 'said arms, each of said clamp members having its marginal portion adjacent the leading edge of its respective arm folded upon itself to provide a generally U-shaped configuration, a flexible fan blade extending into each of said clamp members, a backing plate overlying each of said blades and extending into said clamp member, and fastening means spaced 3 along the length of each arm to rigidly join the arm, clamp member, blade [and backing plate, whereby stress in the blades due to flexing of the blades and the backing plates is more evenly distributed across the width of the blade and stress concentration at said fastening means is 5 avoided.

References Cited by the Examiner UNITED STATES PATENTS 4 Bouvy et al 103115 Jandasek 103115 Senn 103ll5 Posh 103--115 FOREIGN PATENTS Great Britain.

MARK NEWMAN, Primary Examiner.

HENRY F. RADUAZO, Examiner. 

1. A FAN STRUCTURE INCLUDING A SPIDER HAVING ARMS EXTENDING RADIALLY OUTWARD FROM A CENTRAL HUB PORTION, CLAMP MEMBERS OVERLYING ONE FACE OF EACH OF SAID ARMS AND EXTENDING BEYOND THE ENDS OF SAID ARMS, EACH OF SAID CLAMP MEMBERS HAVING ITS MARGINAL PORTION ADJACENT THE LEADING EDGE OF ITS RESPECTIVE ARM FOLDED UPON ITSELF TO PROVIDE A GENERALLY U-SHAPED CONFIGURATION, A FLEXIBLE FAN BLADE EXTENDING INTO EACH OF SAID CLAMP MEMBERS, A BACKING PLATE OVERLYING EACH OF SAID BLADES AND EXTENDING INTO SAID CLAMP MEMBER AND SUBSTANTIALLY TO THE TRAILING EDGE OF THE ARM, AND FASTENING MEANS SPACED ALONG THE LENGTH OF EACH ARM TO RIGIDLY JOIN THE ARM, CLAMP MEMBER, BLADE AND BACKING PLATE, WHEREBY STRESS IN THE BLADES TO FLEXING OF THE BLADES AND THE BACKING PLATES IS MORE EVENLY DISTRIBUTED ACROSS THE WIDTH OF THE BLADE AND STRESS CONCENTRATION AT SAID FASTENING MEANS IS AVOIDED. 